Cesarean scar niche: comparison of transvaginal ultrasound findings and uterine tissue samples after hysterectomy

Abstract

Background: The cesarean scar niche, a consequence of incomplete wound healing, can lead to gynecological complications and affect future pregnancies. While internal niches have been well-studied, external and bidirectional niches are also important.

Objective: We aimed to conduct a comparative analysis of the prevalence and measurements of different types of niches.

Study design: This cross-sectional study examined 200 patients with prior cesarean delivery undergoing hysterectomy due to abnormal uterine bleeding. It evaluated internal, external, and bidirectional niche prevalence, measurements (height, residual myometrial thickness, and adjacent myometrial thickness), and classification in hysterectomy specimens compared to prehysterectomy transvaginal sonography reports. The secondary outcome was to determine niche presence in uterine tissue samples based on the number of previous cesarean deliveries.

Results: The mean age of the study participants was 48.19 years, with 30% having undergone only one cesarean delivery. Notably, 83.5% had niches detected via sonography, while 91% had niches identified in uterine tissue samples posthysterectomy (P value=.008). Internal niches were common, with significant associations between niche presence and the number of previous cesarean deliveries. 23.3% of patients with one cesarean delivery had internal niches. Additionally, external niches were detected in 4% of hysterectomy samples but not observed in ultrasound reports. Key parameters such as residual myometrium thickness and adjacent myometrial thickness differed notably between ultrasound and tissue samples, highlighting discrepancies in niche detection methods. Residual myometrium thickness ranged from 2.8 to 24 mm (7.68±3.09 mm) in ultrasound reports vs 0 to 25 mm (4.28±2.71 mm) in tissue samples (P<.001). Adjacent myometrial thickness ranged from 6 to 29 mm (17.08±4.53 mm) in ultrasound reports vs 7.5 to 30 mm (16±5.03 mm) in tissue samples (P<.001). This study underscores the importance of accurate niche assessment in patients with prior cesarean delivery.

Conclusion: We performed a comparative analysis of niche prevalence and measurements in gross specimens and transvaginal sonography reports. The results highlight the importance of considering external and bidirectional niches, in addition to internal niches. These niches can reduce residual myometrial thickness and increase future pregnancy complications. Furthermore, we demonstrated that niche formation can occur after a single cesarean delivery.

Keywords: bidirectional niche; cesarean scar defect; external niche; internal niche; isthmocele; residual myometrium thickness; transvaginal sonography.